In an underground mine the miner must constantly be concerned about the structure over his head, inasmuch as the mine is cut through the ground and a tremendous mass of rock or earth overlies the horizontal portion of each mine. To attempt to secure the overhead against unexpected falls, miners have developed a methodology by which the mine roof is ostensibly supported. Holes are drilled into the roof and a plurality of anchors on substantial metal rods are inserted into the holes. A compression plate is secured to the bolts beneath the roof and as the anchors tighten against the compression plate the anchors serve to provide a region of increased compression which acts to bind the stratus of rock into a beam supporting the remainder of the roof.
Mine roof anchors inserted into a pre-drilled hole have been the subject of numerous patents. Patents exist on anchors which have serrated outer shells, which have bails, which have a plurality of wall engaging members formed in a stack, and which have numerous other configurations.
It appears that the anchors of the past have tended to fracture the wall surrounding the hole incorrectly, using a plurality of serrations or plates to fracture the wall at varying heights about the anchor during the process of compressing the wall to prevent dislodging of the anchor. As the wall is fractured the tendency for the wall to crumble has not been restrained thus rock particulate moves in the path of least resistance; thus into bore holes beneath the multiple fractures. As a result, the roofs supported by the anchors of the day continue to fall, endangering lives and reducing the efficiency of the mining operation.